In recent years, a capsule endoscope appears in the field of endoscope. The capsule endoscope is equipped with an imaging function and a radio communication function. The capsule endoscope is swallowed from a mouth of a subject for an observation (examination). After being swallowed, the capsule endoscope moves through inside internal organs (body cavities), such as a stomach and a small intestine, following a peristaltic motion inside the subject, and sequentially picks up images inside using the imaging function until being naturally discharged from a living body of the subject (human body), i.e., during an observation period.
While moving inside the internal organs, i.e., during the observation period, the capsule endoscope sequentially transmits image data obtained through imaging inside the body cavities to an outside of the subject using the radio communication function. The transmitted image data is stored in a memory provided inside a receiving device outside. After swallowing the capsule endoscope, the subject carries the receiving device which has radio communication function and memory function until the capsule endoscope is discharged, whereby the subject can move freely without inconveniences even during the observation period. After the observation, a doctor or a nurse can retrieve the image data stored in the memory of the receiving device and watch images inside the body cavities on a display device such as a monitor to make diagnosis.
Generally, the receiving device includes plural antenna elements for receiving image signals transmitted from the capsule endoscope. The antenna elements are arranged in a dispersed manner outside the subject. The receiving device selectively switches to one antenna element, which receives image signals with less reception errors, and uses the selected antenna element for reception. For example, a receiver described in Patent Document 1 has plural antenna elements including adhesive applied thereto. The plural antenna elements adhere to the subject at predetermined positions and thereby arranged outside the subject. The receiver switches from one antenna element to another for reception, and locates a position of the capsule endoscope which is a sender of the image signals and placed inside the subject based on intensities of electric fields received by the respective antenna elements.
Patent Document 1: Japanese Patent Application Laid-Open No. 2003-19111